1. Field
Aspects of the present invention relate to an organic light-emitting diode.
2. Description of the Related Art
Organic light-emitting diodes (OLEDs), which are self-emitting devices, have wide viewing angles, excellent contrast, quick response times, high brightness, excellent driving voltage characteristics, and high response rates, and can also realize full color images. Conventional OLEDs may include an anode formed on a substrate, and a hole transport layer (HTL), a emissive layer (EML), an electron transport layer (ETL), and a cathode sequentially, formed on the anode. The HTL, the EML, and the ETL are organic thin films including organic compounds.
When a voltage is applied between the anode and the cathode, holes injected from the anode move to the light-emitting layer, via the hole transport layer, and electrons injected from the cathode move to the emissive layer, via the electron transport layer. The electrons and holes recombine in the light-emitting layer to generate excitons. Light is emitted when the excitons transit to a ground state from an excited state.
The luminescent efficiency of an OLED may be categorized into an internal luminescent efficiency and an external luminescent efficiency. The internal luminescent efficiency is influenced by how efficiently excitons are generated and converted into light, in the organic layers, such as the HTL, the EML, and the ETL. On the other hand, the external luminescent efficiency (also referred to as “light coupling efficiency”) is influenced by how efficiently light generated in the organic layers is extracted from of the OLED. The total luminescent efficiency of an OLED is reduced, if the external luminescent efficiency is low, even if the internal luminescent efficiency is high. High-quality OLEDs should have a wide viewing angle as well as a high light coupling efficiency.